The present invention relates to a railroad track ballast tamper of the forced vibration type.
In the field of railroads, it is necessary to consolidate the tracks by packing the cross ties using a method known as tamping. This consists in packing the ballast under the cross ties using devices known as tampers which are, in fact, vibrating grippers. These are forced into the ballast, on each side of a cross tie, causing the latter to vibrate at a given frequency close to the natural frequency of the ballast, and imparting to the gripper a closure movement which forces the ballast in under the cross tie.
FIG. 1 of the appended schematic drawing shows a current design of tamper. This comprises a chassis 1 equipped with vertical suspension elements 2 and 3 and two tool holders 4 and 5 articulated symmetrically to the chassis 1 about two respective parallel and horizontal axles 6 and 7, in the manner of levers. In their upper parts, the two tool holders 4 and 5 are equipped respectively with tools 8 and 9 known as xe2x80x9cpackersxe2x80x9d, which fit on each side of a cross tie 10 of the track. A device involving an eccentric 11, carried by the central part of the chassis 1, causes the tools 8 and 9 to vibrate.
The respective upper ends of the two tool holders 4 and 5 are connected by a roughly horizontal hydraulic gripper ram 12, the body 13 of the ram 12 being, for example, connected by an articulation 14 to the first tool holder 4, while the rod 15 of this ram 12 is connected by an articulation 16 to the second tool holder 5.
An auxiliary hydraulic ram 17 is currently associated with the hydraulic gripper ram 12 and, in combination with a pivoting rider 18, acts as a mechanical stroke limiter for the gripper ram 12, as depicted more particularly in FIGS. 2 and 3. The auxiliary ram 17 is articulated by its body, about an axle 19, to the body 13 of the gripper ram 12, toward one end of this body 13. The rod of the auxiliary ram 17 is articulated, about an axle 20, on the rider 18 which is itself mounted so that it can pivot about an axle 21 on the body 13 of the gripper ram 12, toward the other end of this body 13.
In a first position illustrated in FIG. 2, the auxiliary ram 17 (the rod of which is deployed) brings the rider 18 into direct abutment on the front face of the body 13 of the gripper ram 12, by pivoting about the axle 21. The rider 18 thus positioned constitutes a blocking wedge which limits the opening stroke of the gripper ram 12 to a value C1, by a mechanical stop effect. This first position, in which the opening gripper stroke of the vibrating gripper is limited, is suitable for the use of the tamper with a single cross tie 10.
To deal with a double cross tie, formed of two cross ties back to back, as encountered in particular where rails join, the auxiliary ram 17 is actuated in the direction of retraction of its rod so as to cause the rider 18 to pivot about the axle 21 in the direction of its retractionxe2x80x94see FIG. 3. The rod 15 of the gripper ram 12 can therefore describe its maximum stroke C2 until this rod 15 is fully retracted into the body 13 of the gripper ram 12. Thus the gripper opening stroke is no longer limited and the packers 8 and 9 can be parted more widely so as to grip a double cross tie.
This mechanical stop device causes jolts and noise which, added to the vibration needed for actual tamping and amplified by this vibration, gives rise to a high noise level when the tamper is in operation. This high level of noise is a nuisance not only to the operators, but also to the neighborhood, particularly when the work is carried out at night.
More particularly, the current device for mechanically limiting the stroke of the gripper ram 12 gives rise to mechanical jolts throughout the vibration phase. The mechanical jolts, which are already in themselves noisy, are amplified by the excitation, at the vibrating frequency of the tamper, of the play in the articulation along the three axles 19, 20 and 21 of the assembly made up of the ram 17 and of the rider 18. This phenomenon considerably increases the amount of noise generated by the tamper.
An object of the present invention is to eliminate the jolts, parasitic vibration and noise generated by the device for mechanically limiting the opening stroke of the gripper ram in such a way as to reduce the total level or acoustic emissions of the tamper so as to bring these emissions down to a level that is more acceptable to operators and to the neighborhood.
To this end, a subject of the invention is essentially a ballast tamper of the type involved here, that is to say comprising two tool holders, articulated to a chassis about parallel horizontal axles, which are equipped in their lower parts with tools capable of fitting one on each side of a single or double cross tie of the track concerned, and the upper ends of which are connected by a hydraulic gripper ram, means being provided for vibrating the tools, this ballast tamper being characterized in that the supply of hydraulic fluid or the draining of hydraulic fluid from the hydraulic gripper ram, for at least one of its two directions of travel, is provided by a hydraulic assembly external to this ram and comprising means for metering an amount of hydraulic fluid capable of being let into said ram or discharged therefrom so as to cause the rod of this ram to describe a gripper opening stroke limited to a value below that of its full stroke, the hydraulic assembly also comprising hydraulic control means associated with said metering means.
In one embodiment of the invention, the means for metering the amount of hydraulic fluid let into the gripper ram or discharged therefrom consist of a metering ram, the piston of which can be moved hydraulically over a controlled stroke, it being possible to place said metering ram in communication with the gripper ram so as to allow a predetermined amount of hydraulic fluid to be let into or drained from this gripper ram.
Thus, the inventive step consists in replacing the current mechanical stop device that limits the opening stroke of the gripper ram with an assembly which produces a kind of xe2x80x9chydraulic stopxe2x80x9d effect, by metering the amount of oil used in the gripper ram. By virtue of appropriate control means, this ram can be supplied with or drained of hydraulic fluid either directly, in which case it will effect its full opening stroke, designed for use of the tamper with double cross ties, or indirectly with the intervention of the metering ram, in which case the gripper ram describes a limited opening stroke designed for use with single cross ties.
Thus, the mechanical elements located on the tamper and which generate jolts and noise, namely the pivoting rider and its actuating ram, are dispensed with entirely, thus definitively eliminating the noises emitted by these elements and by their articulations In addition, the elimination of these mechanical components simplifies the structure and the kinetics of the tamper.
As a preference, the hydraulic assembly including the metering means such as the metering ram and the hydraulic control means associated with said metering means is located some distance away from the hydraulic ram in a fixed, non-vibrating part of the machine. The metering ram, which is therefore located at a stable point, generates no mechanical noise. All of this plays a part in reducing the acoustic nuisance.
As for the hydraulic control means associated with the metering means such as the metering ram, these can be produced in a simple way using a set of directional-control valves, particularly electrically-operated directional-control valves designed to selectively direct the hydraulic fluid directly to the gripper ram or to the metering means or to selectively drain the gripper ram directly to the source of fluid or to the metering means.